In a method for identifying a unit in a solid state memory device for writing data to a tier structure is maintained the tier structure comprising at least two tiers for assigning units available for writing data to. In response to receiving a request for writing data it is determined if a unit for writing data to is available in a first tier of the at least two tiers. In response to determining that a unit is available for writing data to in the first tier this unit is identified for writing data to, and in response to determining that no unit is available for writing the data to in the first tier it is determined if a unit is available for writing data to in a second tier of the at least two tiers subject to a priority of the write request.